The testing of the timing of spark ignition in an internal combustion engine is normally accomplished by means of a mark on the engine flywheel or vibration damper which, when lined up with a reference mark, indicate the top dead center position of a piston in its cylinder. The mark on the rapidly rotating flywheel is observed by a stroboscopic light which is controlled by the engine ignition system. The test requires considerable skill, and is undesirably time consuming.